Vaccinating poultry could actually make the spread of deadly strains of bird flu such as H5N1 worse.
An Edinburgh University study concluded that, unless 95 percent of a given flock has been protected, the disease is more likely to spread. The study used mathematical simulations to calculate the spread of the avian flu among flocks of 10,000 caged birds.
Immunized birds can still catch and transmit avian flu, but do not show any symptoms. Therefore, it becomes harder to detect the spread of avian flu in a vaccinated flock.
It is extremely difficult to protect more than 90 percent of the birds in any given flock, and protection levels are usually even lower than that. In addition, even when 90 percent of the birds are vaccinated, the risk of an outbreak is cut, at best, in half.
Incomplete vaccination could result is the bird flu virus contaminating the birds' surroundings without farmers or authorities realizing it.